Thin wall container with strengthening and insulating characteristics



Nov. 30, 1965 B. EDWARDS 3,220,595

THIN WALL CONTAINER WITH STRENGTHENING AND INSULATING CHARACTERISTICSOriginal Filed Dec. 10, 1959 4 Sheets-Sheet l INVENTOR. Bryan! EdwardsBY EXTRUDER MOLDING ROLL Nov. 30, 1965 B. EDWARDS THIN WALL CONTAINERWITH STRENGTHENIN INSULATING CHARACTERISTICS Original Filed Dec. 10,1959 G AND 4 Sheets-Sheet 2 N 00 Wow 9 INVENTOR. Bryanf Edwards Nov. 30,1965 B. EDWARDS 3,220,595-

THIN WALL CONTAINER WITH STRENGTHENING AND INSULATING CHARACTERISTICSOriginal Filed Dec. 10, 1959 4 Sheets-Sheet 3 INVENTOR. Bryan/ EdwardsNov. 30, 1965 B. EDWARDS 3,220,595

THIN WALL CONTAINER WITH STRENGTHENING AND INSULATING CHARACTERISTICSOriginal Filed Dec. 10, 1959 4 Sheets-Sheet 4 o q N mmvron. A 3 BryantEdwards BY k air United States Patent THIN WALL C(PNTAHNER WITHSTRENGTHEN- ING AND INSULATING CHARACTERISTICS Bryant Edwards, ClarendonHills, IlL, assignor to Illinois Tool Works Inc., a corporation ofDelaware @riginal application Dec. 10, 1959, Ser. No. 858,792, now

Patent No. 3,141,913, dated July 21, 1964. Divided and this applicationNov. 27, 1963, Ser. N 0. 326,487

6 Claims. (Cl. 2209) This is a divisional application of Serial No.858,792, filed December 10, 1959, now Patent No. 3,141,913.

This invention relates in general to containers, and more particularlyrelates to plastic containers which are of the thin wall variety.

It has been desired to have an economical plastic container for use withhot beverages, foods, etc. and of the type wherein the user is notsubjected to discomfort from heat transfer of a hot beverage disposedwithin the container.

It is therefore the general object of this invention to provide aplastic container which, when filled with hot beverages, may be readilymanually grasped without discomfort to the user while drinking from orcarrying the container.

Another object of this invention is to provide an economical plasticcontainer of the aforementioned type which may be stacked and readilydispensed from a vending machine, being comparable in weight to presentcup designs.

It is another object of this invention to provide a unitary plasticcontainer which is unaffected by humidity and thus is dimensionallystable for easy vending, is uniform in size when manufactured by massproduction techniques, and is otherwise well adapted to be automaticallyvended from the vending machines now in use.

It is another object of this invention to provide a corn tainer as abovedescribed which is strong per unit of weight, has no seams todisintegrate when filled with a hot beverage, and has a configurationaffording insulating characteristics such that it may be readily held byuser when the temperature of the beverages contained therein are wellabove the temperature that the human hand can normally withstand.

It is a further object of this invention to provide a novel container asset forth above which protects table surfaces, etc. from heat transfer,and additionally, the very low moisture vapor transmission of thematerial protects the table surface, etc. from marking by the beveragescontained therewithin.

Another object of this invention is to provide a container comparable inweight to containers heretofore known, but wherein the formed materialaffords a greatly increased apparent thickness of the container tothereby insulate the user from the temperature of the contents in thecontainer.

Another object of the invention is to provide a container asaforedescribed which is made of similar base material to prior artcontainers but, due to configuration of materials, is stronger per unitof weight than containers known heretofore.

Other objects and advantages of the present invention will appear fromthe following description in the accompanyin g drawings wherein:

FIG. 1 is a fragmentary perspective view of a portion of the apparatusand materials being made by the process shown in FIG. 2;

FIG. 1a is a fragmentary sectional View of the material shown in FIG. 1;

FIG. 2 is a semidiagrammatic showing of the components of apparatus usedin manufacturing the materials shown in FIG. 1;

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FIG. 3 is an isometric perspective view of the continuous molding rollused in the apparatus shown in FIG. 2;

FIG. 4 is an enlarged fragmentary sectional view of a portion of theroll shown in FIG. 3;

FIG. 5 is an isometric perspective view, a portion being in section,illustrating somewhat diagrammatically a container embodying principlesof this invention;

FIG. 6 is a side view of the container shown in FIG. 5;

FIG. 7 is a bottom view of the container shown in FIG. 6;

FIG. 8 is an enlarged fragmentary sectional view of the upper portion ofa container such as shown in FIG. 5 when made of the materials shown inFIG. 9;

FIG. 9 is a fragmentary isometric perspective view of the material usedin making the container shown in FIG. 8;

FIG. 10 is a view similar to FIG. 8 when utilizing the materials shownin FIG. 11;

FIG. 11 is a fragmentary isometric perspective view of the material usedin manufacturing the article shown in FIG. 10;

FIG. 12 is an isometric perspective view of an alternate type ofmaterial being manufactured by the general process shown in FIG. 2;

FIG. 13 is a view similar to FIG. 12 of still another type of materialusable in making containers embodying the inventive concepts;

FIG. 14 is a semidiagrammatic isometric perspective view, a portionbeing in section, indicating diagrammatically the form of a containerthat is obtained when the material shown in FIG. 12 is used;

FIG. 15 is a fragmentary sectional view of an upper portion of thecontainer shown in FIG. 14 when a portion of the material shown in FIG.12 is used in a nonlaminated form;

FIG. 16 is a view similar to FIG. 15 showing the upper portion of thecontainer when a laminated material such as shown in FIG. 12 isutilized;

FIG. 17 is a semidiagrammatic view, of the apparatus utilized in thepreferred method of molding containers from the materials shown in theearlier figures.

Before discussing the invention in detail some general background wouldappear beneficial. Plastic containers have begun to come into generaluse with automatic vending machines and (particularly when associatedwith hot beverages such as coffee, soup, etc.) present a handling orholding problem to the user when the beverage is served hot.

Most of the plastics used in manufacturing these containers have fairlygood insulating characteristics per unit thickness when compared withother materials. However, in the interests of economical manufacture ofplastic containers to compete successfully with other materials,relatively thin walls are required, since raw plastic material isuniformly sold on a per pound basis, and increasing of the amount orthickness of the material to increase the insulating qualities wouldmerely increase the unit price of a plastic container to make itnoncompetitive. One approach to the problem has been to try to extendthe plastic material by foaming, i.e., creating bubbles of gas in theplastic material, and manufacturing a container of such foam material ormanufacturing a laminate of foamed material to a thin web of non-foamedmaterial. This approach to date has not proved successful in terms ofacceptable containers at a competitive price to containers made fromother materials. Further, laminated foam and sheet stock pose greatproblems in reconstituting the scrap material. Also, solid foamcontainers present a product having a non-smooth interior surface whichtraps the particles in suspension in the beverage or the like served inthe container Which is undesirable from a users standpoint.

In my co-pending application entitled Container Molding Machine filedDecember 7, 1962 with Serial No. 243,166 as a continuation of abandonedapplication Serial No. 763,668 filed September 26, 1958, now Patent No.3,172,159, I have disclosed a machine and method for manufacturing thinwall containers by a technique which includes the use of a combinationof mechanical plugassist and pressure differentials. While the instantinvention has special advantages when made through the use of moldingtechniques, it will be apreciated that it also has advantages relativeto the other forming techniques now in use such as vacuum forming, blowforming, drape forming, and the like.

More particularly, I have developed a new material, in the sense that Iincrease the apparent thickness of the material prior to the containermolding stage by premolding, preferably in a continuous manner, aplurality of closely spaced projections on a web of plastic material.This material may then be used as is in the container molding operationor a thin sheet may be laminated to the end portions of the projections.If the projections are configured corectly, not only is the apparentthickness of the finally formed container increased, but in addition,the projections serve to structurally increase the strength and rigidityof the container affording an even further benefit in the weight vs.strength ratio.

The molding of the container with my premolded material utilizes thegeneral techniques taught in the Patent No. 3,172,159 with certainmodifications. These modifications do not change the basic procedure,however, they do aid in providing a better container with certain of thematerials as will be discussed hereinafter.

Returning now to FIG. 2 of the drawings, a first extruder ofconventional design is shown diagrammatically in the lower right handportion of FIG. 2 and is adapted to extrude a uniform web of thinplastic material 12 having a predetermined thickness and width. In theillustration to be described, the plastic material is preferablypolystyrene or a similar type of thermoplastic material. The web 12 isfed between a smooth roll 16 and a molding roll 14 (to be laterdiscussed in detail) from which it emerges in the form which is shown inFIG. 1 and identified with the reference numeral 18. It should be notedthat neither the width or length of the material is increased, but theapparent thickness is grealy increased. The material 18 is then eitherused as is or fed between two laminating rolls 20 and 22 and emerges asa laminated material 24 on the output side of the rolls 20 and 22. Inthe event that laminated material is desired, material which is to belaminated to the premolded material 18 may be conveniently extruded froma second extruder 26. The web passes between two rolls 32 and 34 whichlocate the web 30 for feeding to the area between the laminating rolls20 and 22. The web of material 30 and the premolded material 18 areheated by a suitable heater 28 immediately adjacent the input side ofthe laminating rolls 20 and 22 so as to prepare the surfaces thereofsufliciently to obtain good cohesive bond therebetween in the finallyproduced material 24. Heater 28 may be an electrical resistance type ofheater of any commercially known type or other suitable equivalent typeheater, the main purpose being to soften the mating surfaces only, ofthe material 30 and the premolded material 18. The premolded material18, or the laminated material 24, as it is received from the laminatingrolls 20 and 22, may be wound on a suitable storage roll or may be feddirectly into a container molding machine (shown diagrammatically inFIG. 17) as suitable and desired.

The continuous molding roll 14 is shown in an enlarged fragmentarysectional view FIG. 4 and shown in perspective in FIG. 3. The moldingroll 14 is generally cylindrical and on the outer surface of theperiphery are a plurality of projecting lugs 38. Each of the lugs 38have a generally planar rectangular end surface 40 and four taperingside walls 42, 44, 46 and 48 which taper inwardly in converging relationas they project from the surface of the roll 14. The individual lugs 38may conveniently be formed by cutting away material from a cylinder toform a plurality of axially aligned longitudinal grooves 50 andtransverse circumferential grooves 52. It will be appreciated that thefragmentary sectional view FIG. 4 is considerably enlarged for purposesof clarity as are the certain other views in these drawings inasmuch asit is intended that the individual lugs project from the surface on theorder of five to fifty thousandths of an inch. It will be furtherappreciated that the material 12, material 18, and material 24 are allmeasured in terms of thousandths of an inch and that the final dimensionof the thickness of the side walls of the container 62 used forillustration, would not generally exceed sixty thousandths of an inch.

The molding roll 14 as it impinges upon the material 12 as it comes fromthe extruder 10 (in a heated condition), continuously molds a pluralityof pockets 49 which are complementary in shape to the shape of the lugs38. It should be noted at this time that extreme care must be exercisedso that the lugs 38 on the molding roll do not have any sharp burrs orwire edges so as to tear the corners of the pockets 49 when the moldinglugs 38 are withdrawn from the material as it passes thereby.

As shown in FIG. 1, the material 18 as it leaves the molding roll 14 hasa smooth bottom surface 56 on one side of a base portion 54 and aplurality of projecting cross connecting webs 58 and 60 which correspondrespectively to the valleys or grooves 52 and 50 in the molding roll 14.It will be noted that this premolding operation by the molding roll 14increases the apparent thickness of the material as is shown by therelative thickness of the material 12 before it passes roll 14 and thethickness of material 18 after passing roll 14, best seen in FIG. 2 ofthe drawings. It is preferred that the preformed material 18, in crosssection, presents web members 58 and 60 which are not less in heightthan the bottom wall or base portion 54 is in thickness. The moldingroll 14 is mounted relative to roll 16 and the material 12, and theconfigurations and proportions of the lugs 38 on roll 14 are soarranged, that the material displaced by the lugs fills up the grooves50 and 52 and the top surface of the cross webs 58 and 60 are parallelwith planar surface 56 of the base portion 54.

The material above described, either in laminated form as shown andidentified by the reference numeral 24, or when used in sheet formwithout the laminated element, as shown and identified by referencenumeral 18, is particularly well suited for the manufacture ofcontainers such as 62 as shown in FIGS. 5, 6 and 7. While I have electedto show a container in the form of a cup, it must be realized that theinstant invention is adapted for other uses in molded plastic items andit is not to be limited to the precise article shown.

In container manufacturing of the variety set forth in my co-pendingapplication aforementioned, it is the practice to feed .030 inch webstock into the molding apparatus and the container side walls, aftermolding, are in the neighborhood of .012 inch in thickness. Using thesame starting thickness (and weight) of the material 12 (.30 inch) as itcomes from the extruder 10, and then passing it through the molding roll14, it is relatively easy to increase the apparent thickness thereofsuch that the material 18 (unlaminated form) is .060 inch in apparentthickness. This .060 inch material then is reduced to the neighborhoodof .024 side wall thickness in the finished container in the moldingoperation. However, the unit weight of the container remains the same asthe unmodified material now in use. (The same proportions may be used inlaminated form.)

The container thus formed from my premolded mate- 'rial, while weighingthe same as containers produced heretofor'e, is much stronger due to thereinforcing action of the web as shall become apparent. Thus theincrease in apparent thickness enhances not only insulationcharacteristics, but also increases the strength on a unit Weight basis.Further, due to the increase in apparent thickness, the stacking andvending problems of the containers are enhanced. The increase inapparent thickness increases the interference of special stacking ringswhere used, and under some circumstances allows elimination thereof.

Turning now to the container shown, the container 62 is generallycylindrical in shape having a bottom portion 64, a short skirt portion66, a radial shoulder 68 and side walls 70 which taper outwardly to alip portion 72. The shoulder 68 on the interior or inner wall surface ofthe container is adapted to engage an external shoulder of a similarlyconfigured container nested therewithin, the external shoulder beingdefined by the juncture between the bottom portion 64 and the side walls70 of each container. For a specific discussion of the manner in whichthin wall containers can be stacked in non-jamming nested relationshipWithin one another, reference is made to my Patent No. 3,139,213 whichhas matured from original patent application Serial No. 769,057 filedOctober 29, 1958. The lines 74 and 76 are semidiagrammaticrepresentations of the transformation of the cross webs 58 and 60 whichdefine the pockets 49 in materials 18 and 24 as they are distorted toform new pockets 78 in the container molding operation by the method andapparatus shown semidiagrammatically in FIG. 17.

It will be noted by referring to the enlarged fragmentary sectionalviews on FIGS. 8 and 10 respectively that the ribs or webs 56 and 58 ofthe materials 18 and 24 are stretched out proportionately with thethinning down of the other portions of the material when the containeris formed in the container molding operation. In practice, there are inthe neighborhood of two times as many struts or webs 74 and 76 as areshown in FIGS. 5-7. It will be appreciated that each of the individualpockets 78 have the premolded forms shown respectively as 49 in FIGS. 9and 11 respectively as applied to FIGS. 8 and 10.

The material 18 (shown in FIG. 1 1) when used to form a container 62,produces one having the outside appearance of a grid-like network ofprojecting interconnecting web members 74 and 76. The inside surface ofthe container 81] is relatively smooth. Further, the outer surface ofcontainer 62, when manufactured from material 18 and when grasped by auser on the outside thereof, is such that the fingers of the user willbe separated from the interior 80 by the dimension of the base portion54 and by the thickness of the projecting portions 74 and 76. The ribsor webs 74-76 are relatively closely spaced so as to prevent directcontact by the fingers of the user with the base portion 54. Similarstatements are true relative to the material 24 used in the manufactureof the articles shown in FIG. 8 except that there is an additionalthickness of material or 30' which has been laminated to the endportions of the projecting struts or webs. As shown in FIG. la, thematerial 31? may be very thin stock and substantially less than thethickness of the base portion 54. When this form of material is used inthe relative dimensions stated, care must be taken to mold the container62 so that the surface 56 becomes the surface 80 of the container.

Another embodiment of material 82 is shown in FIG. 12 of the drawings.This material is essentially similar to that aforediscussed except thatthe cross or longitudinal ribs 60 have been eliminated and again thismaterial may be used in the laminated form 83 or unlaminated form 85.More particularly, the material 82 comprises a base material which hasbeen premolded by a roll similar to roll 14 so as to have projectinglugs 86. A web of material 30 may be laminated to the top portions ofthe lugs 86 if desired to provide the laminated form. As shown in FIG.

6 14, the material 32 when used to make a container 62 by the apparatusand method shown in FIG. 17 will assume a configuration as shown, andthe lines 88 are semidiagrammatic representations of the distortion ofthe individual projecting lugs 86 of the material 82. When material 82is used in the laminated form (as shown in FIG. 16) it should be notedthat the preferred method of molding the container assures thatindividual elongated compartments or pockets 92 are created by the lip90 being pinched off in the molding operation (to be later described).By this method each pocket 92 between each pair of projecting ribs 88 isseparated from adjacent pockets and from the atmosphere. Thenon-laminated material 85 when molded into a container, a portion beingshown in FIG. 15, is essentially similar to that shown in FIG. 11 withthe elimination of the cross web member 76. Due to the configuration,the webs 88 necessarily strengthen the container on a weight to strengthratio. Further, it is possible to have a lesser amount of material inthe container as compared to using material 18 with only a slight lossin rigidity. The close spacing of the ribs 88 prevents contact of theusers fingers with the base portion of the material to increase theapparent thickness of the material.

Another type of material 94, usable in molding containers to increasethe apparent thickness thereof, is shown in FIG. 13 and comprises a baseportion 96 having cylindrical projecting lugs 98 which may be used as isin form or may have a thin web 30 laminated to the tops of theprojections 98 as shown to form material 93. The lugs 98 increase theapparent thickness of the material 95. Obviously, since the lugs 98 arenot interconnected, the strength advantage noted in previous forms isnot as great. In the laminated form, the material has been demonstratedto be quite strong per unit weight. When molded into a container, thelugs 98 assume positions on the container corresponding to the points ofintersection of the cross webs 74'76 of containers 62.

As shown in FIG. 17, the preferred method of molding is essentially thattaught in my Patent No. 3,172,159 aforementioned. I have elected to showthe material 18 (unlaminated material) shown in FIG. 1 of the drawingsto illustrate the container molding operation. The apparatus 1%essentially comprises a storage roll 102 having material 18 woundthereon which is fed past a suitable heating means 104 into the moldingapparatus per se wherein it is engaged on the upper and lower sides byan upper and lower clamp means 106 and 108. It will be noted that eachof the clamp means 106 and 188 has an aperture 110 and 112 respectively,which are larger than the mold means 114 and mandrel means 116. The moldmeans 114 essentially comprises a male mandrel or plug member 118 andaround the top portion thereof is a combination clamp and cut-off meanswhich is discussed in detail in my co-pending applicationaforementioned. The mold 116 is essentially frusto-conical inconfiguration, and comprises side walls 122, a short radial shoulder126, a short skirt portion and a knock-Out plug 130, the head of whichis adapted, during the molding operation per se to be the bottom of themold cavity. Of special note are the bleed ports 132 which are placedadjacent the bottom of the short skirt portion 128. It will be notedthat there are no other bleed ports in the side walls 122.

In operation, the material 18 is clamped by the opposed clamping means1064198, and the mold means 116 and mandrel means 114 are moved intotelescoped relation, mechanically drawing the material down into themold cavity. Thereafter, an air pressure differential is created so asto move the web from contact with portions of the mandrel member 118 tothe mold side walls 122. At this time air is trapped between theshoulder 126 and the clamping edges of the mold lip 124 and the cutoffand clamp means 120 on the mold 118 so as to provide a resilient backpressure on the material adjacent the side walls 122 preventing theflattening out of the projecting web portions 58 and 60 of the material18 during the molding operation. Since the pressure differentials acrossthe web created in container molding operations of this kind are rathersevere, without the shoulder edge 126 adjacent the skirt portion 128 andthe clamping of the container around the periphery at the lip, theprojecting portions 58 and 60 (and 86) would have a tendency to becrushed and thereby reduce the advantages of the premolding operation.

It will be noted that the material 18 is fed into the machine so thatthe projecting portions 58-60 (also true of projections 86 and 98) arethose portions that engage the cavity side walls 122 in the moldingoperation. When molding a container with laminated material, it is notnecessary to orientate the material if the web 30 is of the samethickness as the base portion of the material.

While I have shown and described certain embodiments of the invention indetail, it is with full awareness that many modifications thereof canoccur and the scope of the invention, therefore, is to be construed onlyin the light of the prior art and the spirit of the appended claims.

What is claimed as the invention is:

1. A thin wall seamless container made from thermoplastic materialcomprising, a hollow body member having a bottom wall and a peripherallycontinuous side wall extending upwardly therefrom which terminates in anopen month, said container having a cross section throughout theperipherally continuous side wall which presents between inner and outerwall surfaces thereof a base portion of predetermined thickness, saidbase portion having uniformly distributed throughout its area aplurality of closely spaced, radially outwardly extending and integralprojecting portions disposed on the outer side wall surface and beingjoined to each other by interconnecting means at points radiallyoutwardly offset from said base portion to strengthen the container,said projecting portions extending outwardly by a dimension at least asgreat as the thickness of the base portion whereby the apparentthickness of the peripherally continuous side wall is increased toseparate the container contents from a users hand by at least double thethickness of said base portion, said base portion throughout at least amajor portion of its height being of uniform thickness with a smoothuninterrupted inner wall surface.

2. The container set forth in claim 1 wherein said interconnecting meanscomprises a plurality of web members similar in size and shape to saidprojecting portions and interconnected to said projecting portions in agrid-like network to define a plurality of closely spaced, discretepockets.

3. The container set forth in claim 2 including a sheet member of apredetermined thickness and of a like material secured to the ends ofthe projecting portions and web members.

4. The container set forth in claim 1 wherein said interconnecting meansincludes a sheet member of predetermined thickness and of a likematerial secured to the ends of the projecting portions in spacedrelation to the base portion to join the projecting portions to eachother.

5. The container set forth in claim 1 wherein at least the projectingportions are curvilinear in shape over the entire side wall to aid inpreventing longitudinal slippage of the container or turning of thecontainer in the hands of a user.

6. The container set forth in claim 1 wherein said peripherallycontinuous side wall tapers outwardly as it proceeds upwardly, saidcontainer further including a stacking ring element provided on the sidewall comprising an internal shoulder and an external shoulder spacedvertically therefrom, the external shoulder of one container beingengageable with the internal shoulder of an identical configuredcontainer in nested relationship therewith to limit the degree oftelescoping of nested containers.

References Cited by the Examiner UNITED STATES PATENTS 2,221,310 11/1940Gazelle 229-3.5 2,530,124 11/ 1950 Kieckhefer 220-97 2,853,222 9/1958Gallagher 2291.5 3,085,730 4/1963 Fibish 229-1.5 3,169,688 2/1965 Schad2291.5

FOREIGN PATENTS 750,189 6/1956 Great Britain.

THERON E. CONDON, Primary Examiner.

GEORGE E. LOWRANCE, LOUIS G. MANCENE,

Examiners.

1. A THIN WALL SEAMLESS CONTAINER MADE FROM THERMOPLASTIC MATERIALCOMPRISING, A HOLLOW BODY MEMBER HAVING A BOTTOM WALL AND A PERIPHERALLYCONTINUOUS SIDE WALL EXTENDING UPWARDLY THEREFROM WHICH TERMINATED IN ANOPEN MOUTH, SAID CONTAINER HAVING A CROSS SECTION THROUGHOUT THEPERIPHERALLY CONTINUOUS SIDE WALL WHICH PRESENTS BETWEEN INNER AND OUTERWALL SURFACES THEREOF A BASE PORTION OF PERDETERMINED THICKNESS, SAIDBASE PORTION HAVING UNIFORMLY DISTRIBUTED THROUGHOUT ITS AREA APLURALITY OF CLOSELY SPACED, RADIALLY OUTWARDLY EXTENDING AND INTERGALPROJECTING PORTIONS DISPOSED ON THE OUTER SIDE WALL SURFACE AND BEINGJOINED TO EACH OTHER BY INTERCONNECTING MEANS AT POINTS RADIALLYOUTWARDLY OFFSET FROM SAID BASE PORTION TO STRENGTH THE CONTAINER, SAIDPROJECTING PORTIONS EXTENDING OUTWARDLY BY A DIMENSION AT LEAST AS GREATAS THE THICKNESS OF THE BASE PORTION WHEREBY THE APPARENT THICKNESS OFTHE PERIPHERALLY CONTINUOUS SIDE WALL IS INCREASED TO SEPARATE CONTAINERCONTENTS FROM A USER''S HAND BY AT LEAST DOUBLE THE THICKNESS OF SIDEBASE PORTION, SAID BASE PORTION THROUGHOUT AT LEAST A MAJOR PORTION OFITS HEIGHT BEING OF UNIFORM THICKNESS WITH A SMOOTH UNINTERRUPTED INNERWALL SURFACE.